The present invention relates generally to bulk acoustic wave resonators and filters and, more particularly, to bulk acoustic wave baluns used in filters and duplexers.
It is known that a bulk acoustic-wave (BAW) device is, in general, comprised of a piezoelectric layer sandwiched between two electronically conductive layers that serve as electrodes. When a radio frequency (RF) signal is applied across the device, it produces a mechanical wave in the piezoelectric layer. The fundamental resonance occurs when the wavelength of the mechanical wave is about twice the thickness of the piezoelectric layer. Although the resonant frequency of a BAW device also depends on other factors, the thickness of the piezoelectric layer is the predominant factor in determining the resonant frequency. As the thickness of the piezoelectric layer is reduced, the resonance frequency is increased. BAW devices have traditionally been fabricated on sheets of quartz crystals. In general, it is difficult to achieve a device of high resonance frequency using this fabrication method. When fabricating BAW devices by depositing thin-film layers on passive substrate materials, one can extend the resonance frequency to the 0.5-10 GHz range. These types of BAW devices are commonly referred to as thin-film bulk acoustic resonators or FBARs. There are primarily two types of FBARs, namely, BAW resonators and stacked crystal filters (SCFs). An SCF usually has two or more piezoelectric layers and three or more electrodes, with some electrodes being grounded. The difference between these two types of devices lies mainly in their structure. FBARs are usually used in combination to produce passband or stopband filters. The combination of one series FBAR and one parallel, or shunt, FBAR makes up one section of the so-called ladder filter. The description of ladder filters can be found, for example, in Ella (U.S. Pat. No. 6,081,171). As disclosed in Ella, an FBAR-based device may have one or more protective layers commonly referred to as the passivation layers. A typical FBAR-based device is shown in FIGS. 1a to 1d. As shown in FIGS. 1a to 1d, the FBAR device comprises a substrate 501, a bottom electrode 507, a piezoelectric layer 509, and a top electrode 511. The electrodes and the piezoelectric layer form an acoustic resonator. The FBAR device may additionally include a membrane layer 505. As shown in FIG. 1a, an etched hole 503 is made on the substrate 501 to provide an air interface, separating the resonator from the substrate 501. Alternatively, an etched pit 502 is provided on the substrate 501, as shown in FIG. 1b. It is also possible to provide a sacrificial layer 506 separating the resonator and the substrate, as shown in FIG. 1c. It is also possible to form an acoustic mirror 521 between the bottom electrode 507 and the substrate 501 for reflecting the acoustic wave back to the resonator. The substrate can be made from silicon (Si), silicon dioxide (SiO2), Gallium Arsenide (GaAs), glass or ceramic materials. The bottom electrode and top electrode can be made from gold (Au), molybdenum (Mo), tungsten (W), copper (Cu), nickel (Ni), titanium (Ti), Niobium (Nb), silver (Ag), tantalum (Ta), cobalt (Co), aluminum (Al) or a combination of these metals, such as tungsten and aluminum. The piezoelectric layer 130 can be made from zinc oxide (ZnO), zinc sulfide (ZnS), aluminum nitride (AlN), lithium tantalate (LiTaO3) or other members of the so-called lead lanthanum zirconate titanate family. Additionally, a passivation layer typically made from a dielectric material, such as SiO2, Si3N4, or polyimide, is used to serve as an electrical insulator and to protect the piezoelectric layer. It should be noted that the sacrificial layer 506 in a bridge-type BAW device, as shown in FIG. 1c, is, in general, etched away in the final fabrication stages to create an air interface beneath the device. In a mirror-type BAW device, as shown in FIG. 1d, the acoustic mirror 521 consists of several layer pairs of high and low acoustic impedance materials, usually a quarter-wave thick. The bridge-type and the mirror-type BAW devices are known in the art.
It is also known in the art that FBARs can be used to form impedance element filters in a ladder filter configuration that has unbalanced input and output ports, or in a lattice filter configuration that has balanced ports. In some applications it would be advantageous to transform an unbalanced input to a balanced output (or vice versa) within a filter. Such filters have been produced using acoustically coupled surface acoustic wave (SAW) resonators. Basically these structures are based on a pair of resonators, as shown in FIG. 2. As shown, the first resonator 620 generates the acoustic wave and the second resonator 630 acts as a receiver. Since the resonators are not electrically connected, one of them can be connected as an unbalanced device and the other can be used in either as a balanced or an unbalanced device. As shown in FIG. 2, the first resonator 620 provides an unbalanced port 622 for signal input, whereas the second resonator 630 provides two ports 632, 634 for balanced signal outputs. As shown, numerals 610 and 640 denote reflectors or acoustic mirrors for the surface acoustic wave device. This same principle can be used in a BAW device having a structure that has two piezoelectric layers, one on top of each other. Using such a structure, it is possible to perform this unbalanced-to-balanced transformation. This structure can then be used as part of a filter or even a duplexer. One possible way of realizing such a structure is described in xe2x80x9cHigh Performance Stacked Crystal Filters for GPS and Wide Bandwidth Applicationsxe2x80x9d, K. M. Lakin, J. Belsick, J. F. McDonald, K. T. McCarron, IEEE 2001 Ultrasonics Symposium Paper 3E-6, Oct. 9, 2001 (hereafter referred to as Lakin). FIG. 3 is a coupled resonator filter (CRF) disclosed in Lakin. As shown in FIG. 3, the CRF is formed by a bottom electrode 507, a bottom piezoelectric layer 508, a cross-over electrode 511, a plurality of coupling layers 512, a ground electrode 513, a top piezoelectric layer 509 and two separate top electrodes 531 and 532. As such, the CRF has a first vertical pair 541 of resonators and a second vertical pair 542 of resonators. Each of the vertical pairs acts as a one-pole filter. In series, the two vertical pairs act as a two-pole filter. The CRF is made on a substrate 501 separated by an acoustic mirror 521. Such a structure requires a considerable amount of substrate area, because the output and input resonators are arranged horizontally side by side. This makes such a filter quite costly.
It is advantageous to provide a method and device capable of transforming unbalanced signals to balance signals wherein the device has a smaller area and a simpler structure.
According to the first aspect of the present invention, a bulk acoustic wave device has a resonant frequency and an acoustic wavelength characteristic of the resonant frequency. The device comprises:
a first resonator having a first electrode, a second electrode and a first piezoelectric layer disposed between the first and second electrodes;
a second resonator having a third electrode, a fourth electrode and a second piezoelectric layer disposed between the third and fourth electrodes; and an electrically insulating layer, wherein the first resonator and the second resonator are arranged in a stack with the electrically insulating layer disposed between the second electrode and the third electrode.
Preferably, the electrically insulating layer comprises a dielectric layer.
Preferably, the dielectric layer has a thickness substantially equal to one half of the acoustic wavelength.
According to the present invention, the device has a signal input end, a first signal output end, a second signal output end and a device ground, and wherein
the first electrode is coupled to the signal input end,
the second electrode is electrically connected to the ground,
the third electrode is coupled to the first signal output end, and
the fourth electrode is coupled to the second signal output end.
Preferably, the device has a capacitive element coupled between the fourth electrode and the device ground for adjusting the parasitic capacitance therebetween. Preferably, the device has an inductance element coupled between the first and second signal output ports, and another inductance element coupled between the signal input port and the device ground for impedance matching and bandwidth widening.
According to the present invention, the first and the second piezoelectric layers each has a thickness substantially equal to one half of the acoustic wavelength.
According to the second aspect of the present invention, a bulk acoustic wave device structure, which is formed on a substrate having an upper section, comprises:
a first electrode provided on the upper section;
a first piezoelectric layer provided on top of at least part of the first electrode;
a second electrode provided on top of at least part of the first piezoelectric layer, wherein the first electrode, the first piezoelectric layer and the second electrode have an overlapping area for forming a first acoustic resonator;
a dielectric layer disposed on top of at least part of the second electrode;
a third electrode disposed on top of at least part of the dielectric layer such that the third electrode and the second electrode are electrically insulated by the dielectric layer,
a second piezoelectric layer provided on top of at least part of the third electrode, and
a fourth electrode provided on top of at least part of the second piezoelectric layer, wherein the third electrode, the second piezoelectric layer and the fourth electrode have a further overlapping area for forming a second resonator.
Preferably, the bulk acoustic wave device structure also has an acoustic mirror structure provided between part of the first electrode and the upper section of the substrate.
According to the present invention, the acoustic wave device structure has a signal input end, a first signal output end, a second signal output end and a device ground, wherein
the first electrode is coupled to the signal input end,
the second electrode is electrically connected to the ground,
the third electrode is coupled to the first signal output end, and
the fourth electrode is coupled to the second signal output end.
According to the present invention, the first acoustic resonator and the second acoustic resonator have a further overlapping area for defining an active area of the bulk acoustic wave device structure. The second electrode has an extended portion located outside the active area, and the fourth electrode has a further extended portion located outside the active area, wherein the extended portion and the further extended portion have yet another overlapping area for forming said capacitive element.
According to the third aspect of the present invention, an acoustic wave apparatus, which is formed on a substrate having an upper surface, has a device ground, a signal input, a first signal output, a second signal output and a device ground. The structure further comprises:
a first bulk acoustic wave device; and
a second bulk acoustic wave device coupled to the first bulk acoustic wave device, wherein
the first bulk acoustic wave device comprising:
a first resonator having a first electrode, a second electrode and a first piezoelectric layer disposed between the first and second electrodes; and
a second resonator having a third electrode, a fourth electrode and a second piezoelectric layer disposed between the third and fourth electrodes, wherein the first resonator and the second resonator are arranged in a stack with a first dielectric layer disposed between the second and third electrode for electrically insulating the second electrode from the third electrode, and the second bulk acoustic wave device comprising:
a first resonator having a first electrode, a second electrode and a first piezoelectric layer disposed between the first and second electrodes; and
a second resonator having a third electrode, a fourth electrode and a second piezoelectric layer disposed between the third and fourth electrodes, wherein the first resonator and the second resonator are arranged in a stack with a first dielectric layer disposed between the second and third electrode for electrically insulating the second electrode from the third electrode, and wherein the fourth electrode of the first bulk acoustic wave device is coupled to the first signal output of the structure,
the fourth electrode of the second bulk acoustic wave device is coupled to the second signal output of the structure,
the first electrode of the first bulk acoustic wave device is coupled to the signal input of the structure and is electrically connected to the second electrode of the second bulk acoustic wave device, and
the second electrode and the third electrode of the first bulk acoustic wave device are electrically connected to the device ground and the first electrode of the second bulk acoustic wave device.
According to the fourth aspect of the present invention, a bulk acoustic wave filter has a signal input terminal, a first signal output terminal, a second signal output terminal and a device ground. The bulk acoustic wave filter comprises:
a balun having at least two resonators in a stacked-up configuration including
a first resonator coupled between a signal input end and the device ground, and
a second resonator coupled between a first signal output end and a second signal output end, wherein
the first signal output end is coupled to the first signal output,
the second signal output end is coupled to the second signal output terminal; and
at least one acoustic filter segment having
a series element having a first end and a second end, and
a shunt element having a first end and a second end, wherein
the first end of the series element is connected to the signal input end of the balun,
the second end of the series element is connected to signal input terminal,
the first end of the shunt element is connected to the second end of the series element, and
the second end (144) of the shunt element (140) is connected to the device ground (12).
According to the present invention, the first resonator (92) of the balun (10) comprises
a first electrode (40) connected to the signal input end (14),
a second electrode (44) connected to the device ground (12), and
a first piezoelectric layer (42) disposed between the first and second electrodes (40, 44), and
the second resonator (94) of the balun (10) comprises
a third electrode (60) connected to the first signal output end (16),
a fourth electrode (64) connected to the second signal output end (18), and
a second piezoelectric layer (62) disposed between the third and fourth electrodes (60, 64), and wherein
the balun (10) further comprises a dielectric layer (50) disposed between the second electrode (44) of the first resonator (92) and the third electrode (60) of the second resonator (94).
According to the fifth aspect of the present invention, a bulk acoustic wave filter (100xe2x80x2) has a signal input terminal (102), a first signal output terminal (104), a second signal output terminal (106) and a device ground (12). The bulk acoustic wave filter further comprises:
at least one acoustic filter segment (150) having
a first terminal (152) coupled to the first signal output terminal (104),
a second terminal (153) coupled to the second signal output terminal (106),
a third terminal (155),
a fourth terminal (156),
a first series element (160) having a first end (162) connected to the first terminal (152) and a second end (164) connected to the third terminal (155),
a second series element (170) having a first end (172) connected to the second terminal (153) and a second end (174) connected to the fourth terminal (156),
a first shunt element (180) having a first end (182) connected to the third terminal (155) and a second end (184) connected to the second terminal (153), and
a second shunt element (190) having a first end (192) connected to the first terminal (152) and a second end (194) connected to the fourth terminal (156); and
a balun (10) having at least two resonators in a stacked-up configuration including
a first resonator (92) coupled between a signal input end (14) and the device ground (12), and
a second resonator (94) coupled between a first signal output end (16) and a second signal output end (18), wherein
the signal input end (14) is coupled to the signal input terminal (102),
the first signal output end (16) is connected to the fourth terminal (156) of the acoustic filter segment (150), and
the second signal output end (18) is connected to the third terminal (155) of the acoustic filter segment (150).
Preferably, each of the first and second series elements in the bulk acoustic wave filter has a first active area and each of the first and second shunt elements has a second active area greater than the first active area in size.
According to the sixth aspect of the present invention, a duplexer comprises
a first port (210);
a second port (220);
a third port (230);
a device ground (12);
a lattice bulk acoustic wave filter (150), disposed between the first port (210) and the second port (220), said lattice bulk acoustic wave filter (150) having
a first end (151), and
a second end (154) coupled to the first port (210);
a balun (10) coupled between the second port (220) and the second end (154) of the lattice filter (150);
a further bulk acoustic wave filter (150xe2x80x2, 250) having
a first end (151, 251) coupled to the third port (230), and
a second end (154, 254) coupled to the second port (220); and
a phase shifting means (242, 244) coupled between the lattice bulk acoustic wave filter (150) and the further bulk acoustic wave filter (150xe2x80x2, 250) for matching the lattice bulk acoustic wave filter (150) and the further bulk acoustic wave filter (150xe2x80x2, 250), wherein the balun (10) having at least two resonators in a stacked-up configuration including
a first resonator (92) coupled between a signal input end (14) and the device ground (12), and
a second resonator (94) coupled between a first signal output end (16) and a second signal output end (18), wherein
the signal input end (14) is connected to the second port (220), and
the first and second signal output ends (16, 18) are connected to the second end (154) of the lattice bulk acoustic wave filter (150).
According to the present invention, the further bulk acoustic wave filter can be a further lattice bulk acoustic wave filter. In that case, the duplexer may comprise a further balun (10xe2x80x2) coupled between the phase shifting means (242) and the further lattice bulk acoustic wave filter (150xe2x80x2), wherein said further balun (10xe2x80x2) having at least two resonators in a stacked-up configuration including
a first resonator (92) coupled between a signal input end (14) and the device ground (12), and
a second resonator (94) coupled between a first signal output end (16) and a second signal output end (18), wherein the signal input end is connected to the phase shifting means (242) and the signal output ends (16, 18) are connected to the second end (154) of the further lattice filter (150xe2x80x2).
According to the present invention, the further bulk acoustic wave filter can be a ladder bulk acoustic wave filter (250). In that case, the duplexer may comprise a further balun (10xe2x80x2) disposed between the ladder bulk acoustic wave filter (250) and the third port (230), wherein said further balun (10xe2x80x2) having at least two resonators in a stacked-up configuration including
a first resonator (92) coupled between a signal input end (14) and the device ground (12), and
a second resonator (94) coupled between a first signal end (16) and a second signal end (18), wherein the signal input end (14) is connected to the first end (252) of the lattice bulk acoustic device (250), and the signal output ends (16, 18) are connected to the third port (230).
According to the seventh aspect of the present invention, a duplexer comprises
an antenna port (220);
a first transceiver port (210);
a second transceiver port (230);
a device ground (12);
a balun (10) coupled between the antenna port (220) and the first transceiver port (210);
a bulk acoustic wave filter (150xe2x80x2, 250) having
a first end (151, 251) coupled to the second transceiver port (230), and
a second end (154, 254) coupled to the antenna port (220); and
a phase shifting means (242, 244) coupled between the balun (10) and bulk acoustic wave filter (150xe2x80x2, 250) for matching the balun (10) and the bulk acoustic wave filter (150xe2x80x2, 250), wherein the balun (10) having at least two resonators in a stacked-up configuration including
a first resonator (92) coupled between a signal input end (14) and the device ground (12), and
a second resonator (94) coupled between a first signal output end (16) and a second signal output end (18), wherein
the signal input end (14) is connected to the antenna port (220), and
the first and second signal output ends (16, 18) are connected to first transceiver port (210).
According to the present invention, the bulk acoustic wave filter can be one or more lattice and ladder filter segments.
According to the eighth aspect of the present invention, a duplexer comprises
an antenna port (220);
a first transceiver port (210);
a second transceiver port (230);
a device ground (12);
a first balun (10) coupled between the antenna port (220) and the first transceiver port (210);
a second balun (10xe2x80x2) coupled between the antenna port (220) and the second transceiver port (230); and
a phase shifting means (242, 244) coupled between the first and second baluns adjacent to the antenna port (220), wherein
the first balun (10) having at least two resonators in a stacked-up configuration including
a first resonator (92) coupled between a signal input end (14) and the device ground (12), and
a second resonator (94) coupled between a first signal output end (16) and a second signal output end (18), wherein
the signal input end (14) is connected to the antenna port (220), and
the first and second signal output ends (16, 18) are connected to the first transceiver port (210); and wherein
the second balun (10xe2x80x2) having at least two resonators in a stacked-up configuration including
a first resonator (92) coupled between a signal input end (14) and the device ground (12), and
a second resonator (94) coupled between a first signal output end (16) and a second signal output end (18), wherein
the signal input end (14) is connected to the antenna port (220) via the phase shifting means (242), and
the first and second signal output ends (16, 18) are connected to the second transceiver port (230).
The present invention will become apparent upon reading the description taken in conjunction with FIGS. 4 to 18.